Caulking for efficency-

Do you want to save the most money on your heating $$ going down the toilet? Insulate well, and replace old doors and windows. It's easy for me to do doors and windows, but some people don't have the dough for the labor.

So if you can't afford that, caulk is your friend. Take some painter's caulk, and caulk all the molding gaps around your door and window molding, and on top of and underneathe the windowsills. Caulk all baseboard moldings where there is a significant gap. If you don't know how to use caulk, learn by practice. Nothing screams "hack" to me more than a sloppy caulk job that looks like a peanut butter sammich.

I like a cup of hot water and a wet rag to smooth the caulk, some guys use spit and their finger, some guys are so good they run their finger once, and it's perfect.

However you do it, get it done, dollars are pouring out of the gaps in your building envelope. Even if you're on a low budget, it's in your power to save yourself some $$.